The U.S. Pat. Nos. 3,935,099, 3,981,100, 3,985,616 and 3,997,484 all issued in 1976 have been given credit for the materials referred to as super absorbent polymers. Since 1976, many inventors have been issued patents for super absorbent polymers (SAP). Most all of these patents claim compositions made by copolymerizing acrylic acid and acrylamide in the presence of a coupling agent. A few of these patents also include a natural polymer such as starch as claimed in U.S. Pat. Nos. 3,935,099, 3,981,100, 3,985,616 and 3,997,484. The patents made without starch refer to their SAP as totally synthetic copolymers. Today the market for the totally synthetic copolymers, SAP, is estimated to be about 2 billion pounds per year worldwide. These SAPs are used almost totally in baby diapers, adult diapers, catamenials, hospital bed pads, cable coating and the like.
Starch graft copolymer compositions with the ability to absorb up to 1000 times their weight in aqueous fluids are known in the prior art. The prior art disclosed cross-linked starch-graft copolymers which absorb large quantities of aqueous fluids for use in absorbent softgoods, in increasing the water holding capacity of soils, and as coatings onto seeds, fibers, clays, paper and the like. The prior art also disclosed methods for drying the compositions to give films by drying in trays, or by heating on drum dryers. These films can then be ground or milled to give flakes or powders. An alternative method for drying was disclosed in the prior art where a viscous mixture of alkali starch-graft copolymer was diluted with a waster miscible organic solvent such as alcohol or acetone. The precipitated alkali starch graft copolymer was then isolated in a fine powder form by filtration and drying.
Surprisingly, agricultural companies that market seed, fertilizer, herbicides, insecticides and other agricultural materials, have found little use for the totally synthetic copolymers (SAPs) in agriculture. In evaluations of SAPs, the SAPs performed poorly and were of no interest to agricultural companies.
It is surprising that the application of starch-containing graft copolymers, made by the methods disclosed herein, directly to the soil resulted in earlier seed germination and/or blooming, decreased irrigation requirements, increased propagation, increased crop growth, increased crop production, and decreased soil crusting. Thus, starch graft copolymers made by the methods disclosed herein have great advantages to assist in agriculture practices and production.
Also surprising was that the prior art dried films or dried powders are not useful in broad scale agricultural applications since these powders are smaller, finer than 80 mesh, in particle size, and are limited to this particle size due to the ways in which these powders are produced. One inherent limitation with finer mesh particles is that they cannot be used in typical granule applicators. The films and powders would not be useful to apply with granule fertilizers, granule pesticides or other granule agricultural additives. In granule applicators, the particle size needs to be somewhat larger, at least about 25 mesh. The starch graft copolymer of this invention provides a commercially viable product for use in broadscale agricultural applications.
In one aspect of the invention, a first method of producing a starch graft copolymer for use in agricultural applications is disclosed. It includes the following steps: (a) providing grafting reactants and a starch; (b) graft polymerizing the grafting reactants onto the starch to form a starch graft copolymer; (c) saponifying the starch graft copolymer; (d) precipitating the starch graft copolymer; and (e) granularizing the starch graft copolymer to form particles.
A second method of producing a starch graft copolymer for use in agricultural applications is also disclosed. It includes the following steps: (a) providing grafting reactants and a starch; (b) graft polymerizing the grafting reactants onto the starch to form a starch graft copolymer; (c) saponifying the starch graft copolymer; (d) adding an acid to lower a pH of the starch graft copolymer to about between 2.0 and 3.5 to precipitate the starch graft copolymer to form a starch graft copolymer precipitant; (e) separating the starch graft copolymer precipitant; (f) neutralizing the pH of the starch graft copolymer precipitant to about between 6.0 and 8.0 to form a starch graft copolymer; and (g) granularizing the starch graft copolymer to form particles.
In another aspect of the invention, methods of using a starch graft copolymer produced by the two methods above, are disclosed to increase crop production. These methods of using include applying the granulated starch graft copolymer directly to the furrow, as well as coating a root or seed with the starch graft copolymer.
In another aspect of the invention, a starch graft copolymer for use in agricultural applications made in accordance with the two methods above is disclosed.
The alkali starch graft copolymers of this invention are produced by graft polymerizing grafting reactants onto a starch. The grafting reactants of this invention include an acrylonitrile and an initiator. The starch may be selected from the group consisting of starches, flours, and meals. The preferred embodiment includes gelatinized cornstarch. The acrylonitrile may be used alone or in conjunction with other monomers commonly used in the industry. The preferred weight ratio of the starch to the acrylonitrile is in the range of about between 1:2 and 1:5. The acrylonitrile is graft polymerized onto starch in the presence of an initiator, preferably a cerium (+4) salt. The preferred initiator is cerium ammonium nitrate. However, other suitable initiator systems are known to those skilled in the art. The polymerization is accomplished in several minutes producing long grafted chains of polyacrylonitrile, or polyacrylonitrile with other monomers attached to the starch. This starch graft copolymer is then saponified with an alkali metal, preferably potassium hydroxide or sodium hydroxide, to change the nitrile groups into a mixture of carboxamides and alkali carboxylates.
The saponification step provides a highly viscous mass that must be isolated in a dry form for usage in agriculture. The resulting saponificate is then precipitated into a solid form and formed into the desired size particles. Formation of the starch-containing graft copolymers into particles of the desired size for direct use in agricultural equipment is achieved by converting the viscous mass of alkali starch-graft copolymers into rod-shaped forms and drying the forms to the desired particle size. Selecting an appropriate die can vary the rod-shaped forms. A plate is used that has been drilled or formed to contain holes of selected size and shape. Rod-shaped forms may be lightly coated, after the die, to reduce the tackiness of the rod-shaped forms. Clays, starches, flours and cellulose can be used to dust the rods.
There are two methods of making the starch-containing graft copolymers of this invention. In the first method, the starch-containing graft copolymer is prepared and rod shapes of the copolymer are formed from the viscous alkali starch graft copolymer. The isolated product is recovered from the viscous polymerization dough with the use of water miscible solvents such as alcohols. These include methanol, ethanol, propanol and isopropanol. Since methanol is generally the least expensive of the alcohols, it is often chosen and it is the preferred alcohol in this method. The resulting dough is then immersed into the alcohol, and the alkali starch graft copolymer is precipitated into particles that are then screened after drying to the desired size. The diameter of the rods is controlled by drilling holes in the end plate of {fraction (1/16)} inch to xc2xc inch diameters. This first method of precipitation by the use of alcohols is very different from the second method of precipitation, which does not use alcohols for precipitation.
A second method of making the starch containing copolymers utilizes another method of precipitating the saponificate. The second method differs from the first method in that it utilizes an acid precipitation, which is then separated in some manner, and then neutralized to produce a viscous mass, which is then formed into rod-shaped particles and allowed to air or oven dry before screening or grinding and screening.
In the second method, after the starch graft copolymer is saponified according to the steps of the first method, the alkali starch graft copolymer is precipitated by adding acid until a pH of about between 2.0 and 3.5, more particularly about 3.0, is reached. The precipitate is washed with water to remove the salts, and if necessary, separated in some manner. Separating methods include settling, centrifuging, and other mechanical means of separating. The carboxylic acid of the starch graft copolymer is then titrated back to the alkali form with the hydroxide of an alkali metal, preferably potassium hydroxide, to a pH of about between 6.0 and 8.0, more particularly about 7.0. This viscous mass is then forced through a die plate; dusted to remove tackiness, and air or oven dried. The dried particles are then screened to the appropriate size. If desired, the particles could be ground to a fine particle then formed into pellets of the desired size for use in agriculture.
For both methods, the final product has a preferred particle size of less than about 200 mesh, depending upon the agricultural application. The preferred particle size for those agricultural applications which deposit the starch graft copolymer directly into the soil with the crop, is less than 50 mesh, more particularly in the range of 8 to 25 mesh. This particle size range is due to the commercially available granule applicators in the industry, which require this larger particle size for application. In order to broadcast or meter the absorbent particle through existing application equipment the 8 to 25 mesh product with a density of 30 to 35 pounds per cubic foot is preferred.
There are other agricultural applications that would use a finer particle size such as seed coating and root dipping. For seed coating, the particle size desired is about between 75 and 200 mesh, more particularly about 100 mesh. For root coating, the particle size desired is about between 30 and 100 mesh, more particularly about 50 mesh.
The results of the product produced by this invention will be demonstrated in the following examples and tables. Particle sizes between about 8 and 25 mesh were evaluated on cantaloupe, cotton and tomatoes with subsequent field evaluations of 40 additional crops. A few pounds/acre of the starch graft copolymer gave excellent results when used as an anti-crusting agent to prevent soil crusting. (See EXAMPLE 5b. and EXAMPLE 6a.) Soil crusting occurs from sprinkler irrigation. When placed on the soil surface prior to the planter press wheel, soil crusting was prevented.
With the starch graft copolymer added as an anti-crusting agent, tomato stand was significantly higher than with the untreated check rows. Tomatoes were also treated below the tomato seed at a 3 to 10 pound per acre rate. Tomato growth was significantly improved with the starch graft copolymer than with the untreated control rows. Tests on cantaloupe showed that the starch graft copolymer caused an earlier than expected blooming, required less irrigation water and gave a substantially greater melon yield of more uniform size and shape of melons that the untreated control group. Tests on cotton demonstrated the starch graft copolymer gave larger cotton plants, even though the cotton plants received one half the amount of water and still gave a 10% increase in cotton lint yield. Tests conducted on over 40 additional crop seeds showed no phytotoxicity from the starch graft copolymer.
In the prior art, the starches claimed were cornstarch, wheat starch, and sorghum starch. In the prior art, the absorbent starch or flour graft copolymers exhibited the ability to absorb a few hundred times to about 1000-times their weight in water. Several starches and flours not previously evaluated for their ability to form absorbent graft copolymers were analyzed and the results are published in TABLE 1. These products were corn meal, peeled yucca root, unpeeled yucca root, oat flour, banana flour and tapioca flour. Absorbent graft copolymers were made from these materials and the water absorbency of each was determined. The absorbent polymers were made with two polymerizable monomers, acrylonitrile and 2-acrylamido-2-methyl-propanesulfonic acid (AMPS) (See TABLE 1). Acrylic acid and acrylamide could also be used in place of AMPS.
Cornstarch graft copolymers made with various levels of acrylonitrile (AN), ceric ammonium nitrate (Ce) and saponified with either potassium hydroxide (KOH) or sodium hydroxide (NaOH) were evaluated also. Useful starches include, but are not limited to, cornstarch, wheat starch, sorghum starch, tapioca starch, cereal flours, and meals, banana flour, yucca flour, and pealed yucca roots. These starch sources are gelatinized to provide the best absorbency. The preferred weight ratio of starch to acrylonitrile is from 1:2 to 1:5. Often the more AN used gives somewhat higher absorbency in the isolated product. The absorbent products were isolated after alcohol precipitation and the absorbencies in the ranges of 400-500 grams of water per gram of polymer to 600-700 grams of water per gram of polymer were found (See TABLE 2).
In the prior art, methanol precipitation has been the solvent of choice to isolate the copolymer into a solid form. It acts to remove the water, desalt and granulize the neutralized alkali starch graft copolymer saponificate into particles. One way is to blend in sufficient methanol into the saponificate until a smooth dispersion is reached. Then the smooth dispersion is pumped into a precipitation tank consisting of a stirring system that can vigorously mix the methanol while pumping in the smooth saponificate dispersion. Once mixed, the resulting methanol and absorbent particles are collected by either (1) decanting or washing with methanol again; or (2) centrifuged and collected then dried to a moisture level about between 1 and 20 percent, more particularly about 10 percent. Although this precipitation method makes an extraneous salt free absorbent particle, there is a wide range of particle sizes formed with a majority of these particles finer than 60 mesh, TABLE 3, NP. These particles are too fine for most broad scale agricultural applications. The fine particles can be pelletized to provide a particle size that would be appropriate for agriculture to use, or they can be used for seed coating or root dipping.
There is another method to precipitate the absorbent polymer with methanol to produce larger particle sizes. The surface of the saponificate is wetted with a small amount of methanol and then chopped into larger xe2x80x9cchunksxe2x80x9d of saponificate that will not adhere back together. Once the surface of the saponificate is wetted with methanol the resulting material is slippery to the touch and is no longer sticky. About between 1 and 2 parts of methanol per 1 part of solids in the saponificate dough achieves this result.
Once this methanol is added the saponificate is either; (1) pumped through an in-line chopper to make chunks less than one inch in diameter or (2) in the laboratory it was hand chopped with scissors. The resulting mixture is then fed into a tank or waring blender that had about between 1.5 and 2.0 gallons of additional methanol per pound of saponificate solids. The methanol in the larger tank is agitated with a Cowles Dissolver or other mixers able to achieve high speeds. Using either: (1) precipitation and decanting techniques; or (2) centrifugation, the resulting particles were dried and sorted by particle sizes. This method produced particles that were much larger than the other means of particle size formation techniques. Typical results showed that using the xe2x80x9cmethanol choppingxe2x80x9d method almost 65 percent of the particles formed were in the 8 to 25 mesh range, TABLE 3, MCM.
Using the experience gained in the methanol chopping method for particle size formation a third method of methanol precipitation was developed. This technique involves pre-forming the particle size diameter prior to methanol precipitation. The use of forming dies to form spaghetti strands of different shapes and diameters greatly improved the particle size formation. With this method one can predict the final particle size by the diameter of the spaghetti formed. The saponificate, neutralized or un-neutralized, is forced through a die plate with holes that varied in diameter from {fraction (1/16)} of an inch to over xc2xc of an inch and of varying shapes for example, round-shaped, star-shaped, ribbons, etc. The method used to force the saponificate through the forming die plate ranged from a hand-operated plunger, screw fed, augured, or pumped or any other similar way to convey the saponificate. The resulting spaghetti strands were formed and allowed to enter into the precipitation tank without any further addition of methanol as a pre-mixing agent. However, wetting the spaghetti strands with methanol or dusting the spaghetti strands with clays or starch or other natural or synthetic polymers would prevent them from sticking together. The resulting spaghetti strands were precipitated with agitated methanol and removed from the tank and dried. Depending upon the diameter of the die plate orifice, the particles formed by this technique were of similar size and shape. Over 85% of the particles were of similar size with very few fines and overs produced, TABLE 3, EP. This method produces a very uniform product that would be used for the agricultural applications.
TABLE 3, MP, shows the results of a fourth method of methanol precipitation. This method included use of a moyno pump, with a variable pump speed, to pump the neutralized saponificate through a plastic pipe with a fixed end cap in which xe2x85x9 inch holes were drilled. The holes can be of any number or pattern that is desired. In this test 50 holes were drilled in the plastic end cap. The end cap was placed several inches above the methanol precipitation tank filled with 50 gallons of agitated methanol. A cover was placed over the precipitation tank and the moyno pump was turned on and the saponificate was pumped through the pipe and forced through the die plate. To prevent the spaghetti strands from swelling after forming due to over pressure of the pump, the pump""s speed was controlled to form spaghetti strands with little swelling. The formed spaghetti strands were immediately immersed in the agitated methanol. After methanol particle forming and the desalting of the polymer, the methanol was decanted off and the remaining polymer was dried to a 10% moisture level. The results of this method of particle size formation are very encouraging for commercial production. The target particle size is reported as 85% of 8 to 25 mesh particle size with just a small percentage of fines. If fines are desired for seed coating or root dipping, then a smaller diameter die plate needs to be used.
In TABLE 3, the dried polymers made by the above methods were passed through a screening system consisting of a 8 mesh screen, followed by a 25 mesh screen, followed by a 60 mesh screen, followed by a 100 mesh screen and a fines collection pan. Upon screening the dried polymer the different cuts were collected and weighed. The percentage of each cut was calculated and reported.
Since some producers of absorbent polymers may not want to use organic solvents such as alcohols to precipitate the copolymers, an alternative method to recover absorbent particles of the desired particle size is disclosed. This alternative method does not use methanol as the precipitating agent. In forming the starch-containing graft copolymer, the alkali saponified starch graft copolymer is produced at a pH of 10 to 12 and then an acid is added to adjust the pH to about between 2.0 and 3.5, more particularly about 3.0. Acids that may be used include inorganic acids such as hydrochloric acid, sulfuric acid or nitric acid, preferably hydrochloric acid. Organic acids such as acetic acid can also be used. This step replaces the alkali in the alkali carboxylate in the graft copolymer with a proton to yield a carboxylic acid in the starch graft copolymer. The alkali forms a salt with the acid added. If the acid is hydrochloric, then potassium chloride and sodium chloride are formed. Any ammonia that is not removed is converted to ammonia chloride if hydrochloric acid is used. This acid treatment of the graft copolymer causes the copolymer to precipitate. The precipitate is then separated by means known to those skilled in the art. Separation may be achieved by any mechanical means, such as settling, filtering, centrifuging, or other means to dispose of the supernatant. The starch graft polymer precipitate is again washed with additional water to remove more of the potassium, sodium or ammonia salts and the supernatant disposed. After most of the salts have been removed by the water washes, the precipitate is then treated with an inorganic base such as potassium hydroxide, sodium hydroxide or ammonium hydroxide. For agricultural uses, the base chosen is generally potassium hydroxide. Potassium hydroxide produces the potassium carboxylate on every carboxylic acid in the starch graft copolymer. A pH in the range of 6.0 to 8.0 is achieved upon adding potassium hydroxide. The potassium hydroxide treatment re-suspends the starch graft copolymer to form a highly viscous mass. In order to dry this mass a pasta maker was used to make rod-shaped extrudates. These extrudates were allowed to air or oven dry. Since the rod-shaped extrudates were sticky, dusting the rods just after they are formed with clay, starches, flours, celluloses, or celite at levels of just a few percent removed the stickiness. The dried rod-shape forms were ground to provide particles of various sizes. If desired, the fine particles could be formed into pellets to provide particles of the preferred size. Pelletizing is common in the polymer industry and known to those skilled in the art.
The initial agricultural tests were conducted using cantaloupe, cotton, and tomatoes with subsequent tests of over forty additional crops.
The Initial Test Methodology:
1. The trial area was pre-irrigated.
2. The plant seed was planted in furrow to moisture.
3. Granule starch graft copolymer treatments were applied in furrow with the seed using a microband, ground-driven granule applicator.
4. Each plant test included 3 plots with the granule starch graft copolymer applied at 7 pounds per acre (LB/a) in one plot, 4 LB/a in another plot, and a control plot.
5. The test bed plants were provided only 50% of the water normally required to grow plants.
6. Evaluations were made at 11, 18, 25, 33, 40, 54, 68, and 75 days.
7. Evaluations included measurements of plant height above the soil level, plant weight cut off at soil level, plant root weight from the cut plants, plant stem diameter, and plant stress level.
8. In the test results, the term xe2x80x9csignificant differencexe2x80x9d was mathematically (statistically) defined.
The cantaloupe in the 7 LB/a plot had a significant increase in plant weight when compared to the control at the 18-day evaluation. Although not always a significant difference, the cantaloupe in the 7 LB/a plot had a greater root and plant weight, stem diameter and plant height at the 25-day evaluation. The cantaloupe in the 7 LB/a plot continued to show less stress and had a greater leaf water potential reading at the 49-day evaluation. The cantaloupe in the 7 LB/a plot began blooming 3 days prior to the control plants. There were considerably more cantaloupe melons harvested form the 7 LB/a plot, the melon weight was greater, and the melons were harvested earlier.
In summary, cantaloupe planted in soil treated with the granule starch graft copolymer (using one half the normal amount of water required to grown cantaloupe) produced larger, healthier cantaloupe that produced more melons, earlier, and at a greater weight than the control plot.
The same methodology was used for the test of the cotton with the exception that the evaluation was conducted at 11, 18, and 25 days; the test was terminated because the cantaloupe plants overgrew the cotton plants. The plots were again provided only one half of the water normally required to grow cotton. The cotton was planted at 1 to 1.5 inches below the surface because cotton will not emerge if planted at a greater planting depth.
Although there was no significant difference in the early growth of the cotton plants, the cotton in the 7 LB/a plot showed better growth in plant height and weight as well as root development. There was a significant difference in the leaf water potential of the cotton planted in the 7 LB/a granule starch graft copolymer plot over the control plot in the 18-day evaluation.
The cotton in the 7 LB/a granule starch graft copolymer plot did indicate increased growth in root length, stem diameter, and plant weight as well as root weight at the 25 day evaluation although the difference was not statistically significant.
Cotton planted in the soil treated with granule starch graft copolymer (using one half the normal amount of water required to grow cotton plants) produced larger, healthier cotton than the control plot. At harvest the cotton lint yield increased from the control plot was 10% greater for the 7 LB/a application rate.
The test methodology for the tomato plants was different than the cotton and cantaloupe.
1. In the 7 LB/a granule starch graft copolymer plot, the granule starch graft copolymer was shanked into the bed approximately 2 inches below the seed.
2. In the 4 LB/a granule starch graft copolymer plot, the granule starch graft copolymer was applied as a surface application in front of the press wheel.
3. The tomato seeds were dry planted as in normal and then sprinkle irrigated to germinate the seed. One problem associated with sprinkle irrigating is that the soil surface crusts and the tomato seed cannot break through the crust.
4. In the tomato test, the plots were evaluated only at 7 days to ascertain the number of germinated seeds that had broken through the crust.
There was a significant increase in the number of emerged tomato plants treated in the 4 LB/a granule starch graft copolymer plot where granule starch graft copolymer was applied at the surface. This application was specifically intended to evaluate the effect of granule starch graft copolymer on plant germination and on soil crusting. It was concluded that granule starch graft copolymer caused small craters in the soil surface, which enabled the tomato plants to emerge. Subsequent tests confirmed the granule starch graft copolymer functions as an extraordinary anti-crusting agent, which is an especially useful characteristic when planting high cost, bio-engineered seeds because this characteristic allows more seed to germinate.
In the second field test on the tomatoes, the tomato plants were allowed to go to harvest. Upon evaluation there was a significant improvement in standing row count with the granule starch graft copolymer treatments when applied over the seed row or as a side-dress treatment when compared to the untreated check. Knowing from an earlier field test that the effect of the granule starch graft copolymer on seed germination and on preventing soil crusting was highly positive, there was a significant increase in yield with the granule starch graft copolymer treated plants when compared to the control check plants. With granule starch graft copolymer applied over the top of the seed row as an anti-crusting agent, the 4 LB/a treatment yielded 38.7 tons per acre as compared to 15 tons per acre for the untreated control. Using granule starch graft copolymer applications as a side dressing below the seed row at the rate of 7 LB/a, yielded 39.3 tons per acre as compared to the control of 15 tons per acre. These higher yields were clearly validated by the initial field test on tomatoes to evaluate the effect of granule starch graft copolymer on plant germination and on soil crusting.
The following examples are intended only to further illustrate the invention and are not intended to limit the scope of the invention, which is defined by the claims.